The present invention relates to a magnetic head having a single magnetic pole head for perpendicular magnetic recording and a method of manufacturing the magnetic head.
Hard disk drives, or magnetic recording and reproducing devices, are primarily used as external storage devices for information processing devices such as computers. As technology evolves, these drives have become larger in capacity and smaller in size. Hard disk drives were primarily developed to improve recording density. If the recording density is increased by using conventional longitudinal magnetic recording, however, the demagnetizing field may become too large in the magnetization transition region of the recording medium. Therefore, there becomes a need to reduce the thickness of the recording layer, which may cause destruction of recorded data due to thermal fluctuations. In perpendicular magnetic recording in which recording magnetization is made in the thickness direction of the medium, on the other hand, a high recording density is easily achieved since demagnetization is small in the magnetization transition region, which alleviates the necessity of reducing the thickness of the medium.
When signals are recorded on a perpendicular recording medium with a magnetic head for perpendicular magnetic recording, namely, a perpendicular magnetic recording head (single magnetic pole head), the electric signals are converted into magnetic signals by a coil. This induces a magnetic flux in a main magnetic pole and a auxiliary magnetic pole. The magnetic flux partially passes from the auxiliary magnetic pole to the main magnetic pole and penetrates the perpendicular recording layer of the medium. The magnetic flux further passes through the soft magnetic underlayer below the perpendicular recording layer and returns to the auxiliary magnetic pole, thus forming a closed loop. The auxiliary magnetic pole serves to return the magnetic flux, which is directed from the main magnetic pole to the perpendicular recording layer and soft magnetic underlayer of the recording medium, and then back to the main magnetic pole in a magnetically effective manner. Using such a magnetic flux flow allows the signals to be recorded as a magnetization on the perpendicular recording layer.
In order to increase recording densities, the recording track width may be reduced. In addition, reading and writing need to be performed on the wide area from the inner circumference to the outer circumference of the recording medium in the hard disk drives. The reading and writing are performed on the inner and outer circumferences of the medium with the skew angle of the magnetic head ranging from about −15° to 15° relative to the tangential line parallel to the rotational direction of the medium. In this case, if the main magnetic pole is rectangular on the air bearing surface, then the recording track widths cannot be reduced. As such, the width of the magnetic pole piece on the leading side becomes smaller than that on the trailing side, thereby achieving narrower track widths.
The main magnetic pole of a recording head may be formed to have a columnar track defining section and a magnetic flux guiding section. The track defining section extends from an air bearing surface in a direction substantially perpendicular to the medium. The magnetic flux guiding section is joined to the track defining section and increased in a cross-sectional area as it is spaced apart from the air bearing surface.
Ion milling is generally used to from the main magnetic pole. Patent document 1 (Japanese Laid-Open Patent No. 2005-216361) describes formation of a main magnetic pole by ion milling. As described in patent document 1, the width of the magnetic pole piece located on the bottom surface of the track-defining section and on the side of a substrate, is progressively narrowed as it becomes close to the air bearing surface. In conjunction with this, the magnetic pole piece width of the upper surface of the track-defining section is progressively narrowed as it becomes close to the air bearing surface. This is due to the shade during ion milling since a mask is formed on the magnetic flux guiding section. With such a structure, if the length of the track defining section from the air bearing surface is varied due to tolerance in the head manufacturing process, this has an adverse effect on the distribution of the magnetic pole piece width of the track-defining surface on the air bearing surface.
In addition, patent document 1 describes a method for improving the structure in which the magnetic pole piece width of the upper surface of the track defining section is narrowed as it becomes close to the air bearing surface. In this method, a nonmagnetic layer or an organic resin layer with a low etching rate is formed on a magnetic layer that serves as the main magnetic pole. Then, etching is performed by ion milling using the nonmagnetic layer or the organic resin layer as a mask while switching the following three processes:
(1) An etching process is performed by setting the incident angle of the ion beam to 50°±20°, and emitting the ion beam while horizontally vibrating the substrate surface in the range of ±(30° to 150°) or from all directions of 360° relative to the direction of the ion beam based on the direction from the medium to the air bearing surface.
(2) Next, an etching process is performed by setting the incident angle of the ion beam to 60°±20°, and emitting ion beams mainly in a range between +90° to +135° based on the direction from the medium to the air bearing surface while horizontally vibrating the substrate surface at a predetermined angle in a range of ±45°.
(3) Lately, an etching process is performed by setting the incident angle of the ion beam to 60°±20°, and emitting ion beams mainly in a range between −90° to −135° based on the direction from the medium to the air bearing surface while horizontally vibrating the substrate surface at a predetermined angle in a range of ±45°.
It is important for the perpendicular magnetic head to cause the recording medium to generate a large recording magnetic field. As described above, reducing the recording track width causes the lowering of a recording magnetic field that is generated from the recording head to the medium side. Accordingly, this needs to reduce the length of the track-defining section from the air bearing surface (the length to a flare point) as well as to reduce the recording track widths. If the length of the track-defining section from the air bearing surface to the flare point is reduced, the upper surface of the main magnetic pole on the air bearing surface that is formed to have a uniform width as with the conventional technique described above largely changes the recording magnetic field in the case where the length of the track-defining section from the air bearing surface varies. This is due to tolerance during the head manufacturing process caused by the varying lengths of the track-defining section from the air bearing surface. Since the width of the recording magnetic field varies at the same time, the track widths to be recorded on the medium are varied consequently.